Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 9.2 — Uses of metals (Part (a), (b))
• Topic 4.2 — Hydrogen-oxygen fuel cells (Part (c))
• Topic 11.1 — Formulae, functional groups and terminology (Part (d))
(a)
For the correct answer:
Al
Aluminium (Al) is widely used in food containers and drinks cans. This is primarily because it is resistant to corrosion due to the presence of a thin, protective layer of aluminium oxide on its surface, which prevents further reaction with air or water.
(b)
For the correct answer:
Au
Gold (Au) is a very unreactive metal. It is placed low in the reactivity series and does not react with water, dilute acids, or oxygen under normal conditions, making it ideal for jewellery and electrical contacts.
(c)
For the correct answer:
O
In a hydrogen-oxygen fuel cell, hydrogen gas reacts with oxygen (O₂) to produce electricity, with water being the only chemical product. Therefore, oxygen is the element that combines with hydrogen.
(d)
For the correct answer:
C
Methane is a simple hydrocarbon with the molecular formula \( \mathrm{CH}_4 \). In this molecule, one carbon (C) atom is covalently bonded to four hydrogen atoms.
